1. Field of the Invention
This invention relates generally to a magnetic head position control system and, more particularly to a system in which the magnetic head employed in recording a magneto-optical disk is driven to maintain a constant distance between the recording surface of the disk and the magnetic head.
2. Description of the Background
In a recording apparatus for a magneto-optical disk in general, an optical head and a magnetic head are disposed in a contact-free fashion on opposing sides of the disk. The recording apparatus operates in accordance with a magnetic field modulation system, whereby a magnetic field corresponding to the recording signal is generated by the magnetic head and applied to the magneto-optical disk, and the area of the disk that is subjected to the magnetic field is heated by a laser beam from the optical head, thereby effecting signal recording.
Because of the information density requirements and the dimensions involved, the laser beam emitted from the optical head must be properly focused onto the disk. The optical head generally controls the focus by collecting focusing data produced by the laser light irradiated onto and reflected from the recording area of the disk, thereby producing a predetermined spot on the recording surface of the disk for recording. By this means, it is possible for the above-described optical head to remain at a constant distance from the magneto-optical disk even when the relative position between the magneto-optical disk and the optical head is changed due to fluctuations in the thickness of the magneto-optical disk, the rotating disk deviates from its in-plane position, or the disk table adapted for rotating the disk is tilted. In the absence of some means for detecting the relative distance between the magnetic head and the magneto-optical disk, the magnetic head must be mounted at a position sufficiently spaced apart from the magneto-optical disk so that the magnetic head will not contact the magneto-optical disk, even when the position of the magneto-optical disk fluctuates in one or more of the above-described fashions.
When the magnetic head is too far away from the magneto-optical disk, the power consumption is disadvantageously increased because the magnetic head must generate a stronger magnetic field for supplying the predetermined recording magnetic field to the recording surface of the magneto-optical disk. In other words, when the separation between the magnetic head and the magneto-optical disk is excessive, an insufficient magnetic field will be applied to the recording surface of the magneto-optical disk, thereby increasing the error rate or lowering the S/N ratio. In the worst of cases, recording may be unfeasible.
For obviating the above inconvenience, an electrode may be mounted on the magnetic head in opposition to the magneto-optical disk for detecting changes in the relative distance between the magnetic head and the disk based on changes in capacitance between the disk and the electrode. The position of the magnetic head may be controlled by the detection output of the electrode for maintaining a constant relative distance between the magnetic head and the disk and to enable the magnetic head to be positioned in the vicinity of the magneto-optical disk. Japanese Patent Application Hei 1-214138 proposes a floating control of a perpendicular magnetic recording system including a disk medium and a stylus, which corresponds to a magnetic head.
However, when the changes in the relative distance between the magnetic head and the disk are measured by the changes in capacitance between the magneto-optical disk and the capacitance detection electrode mounted on the magnetic head, the accuracy of the control of the magnetic head position by the detection output is affected by the linearity of temperature characteristics of the control circuit, so that a predetermined relative distance between the magnetic head and the disk cannot be maintained with accuracy.